This invention is generally directed to a fastener assembly which includes a fastener preassembled to a workpiece. More particularly, the invention contemplates a fastener which is threaded through an initially unthreaded aperture in a workpiece to form a partial thread along the internal surface of the aperture; the fastener having a threaded portion which has a major diameter which is greater than the inside diameter of the aperture and an unthreaded portion which has an outside diameter which is less than the inside diameter of the aperture.
Many users, in particular manufactures in the automobile industry, employ preassemblies wherein a fastener is preassembled to a component used in numerous installations or joints in the manufacture of their products. In some prior manufactures of preassembled fastener assemblies, the fastener assembly generally includes a fastener, such as a bolt, which is initially formed from a blank having an unthreaded portion of a generally constant diameter. After the unthreaded blank is positioned through an unthreaded aperture in a workpiece, the portion of the blank which extends outwardly from the workpiece is subjected to a thread forming process, such as cold rolling wherein a thread or helix is formed on the shank thereof. This type of threading procedure produces an upsetting of the material and reworking thereof to produce a desired thread form. In the cold rolling of the thread, the major diameter of the resulting thread form produced is greater than the original cross-sectional dimension of the unthreaded blank, while the minor diameter is less than the original cross-sectional diameter. This type of product is well-known in the art and is normally referred to as a "sems-type assembly."
A disadvantage in this type of preassembly is that the fastener must be cold worked or rolled after the fastener has been placed through the workpiece, and the size of the workpiece is limited. This increases the cost of manufacture since the thread forming must be done after assembly.
Another type of manufacture for preassembling a fastener to a workpiece is shown in FIG. 1 and will be described in detail herein. Generally, a fastener having a head and an elongate, threaded shank depending therefrom is provided. The threaded shank of the fastener is passed through an unthreaded aperture in a workpiece of any size until the workpiece is positioned adjacent to the head. The unthreaded aperture in the workpiece has an inside diameter which is greater than the major diameter of the threaded shank so that the threaded shank passes freely therethrough.
Thereafter, a push nut is forced over the length of the threaded shank until the push nut lies a predetermined distance from the workpiece. The push nut is generally frusto-conical in shape, and includes a plurality of teeth depending downwardly from a radially outer rim. The teeth contact the threads of the fastener to securely hold the push nut on the fastener. The push nut has an outer diameter which is larger than the aperture in the workpiece so that the fastener can move relative to the workpiece, but remains preassembled.
A significant disadvantage to this type of assembly is that the push nut must be provided which increases the cost of the overall assembly since a component must be provided in addition to the fastener. Additionally, the cost of manufacturing is increased since a push nut must be provided. Furthermore, when the fastener assembly is fastened to a further structure with the push nut being left in the joint, potential problems are created with the clamp load. That is to say that the presence of the push nut in the joint may prevent the workpiece component of the assembly from being properly clamped to the underlying structure.
The novel fastener assembly of the present invention is intended to overcome or minimize these problems and other inherent problems in the prior art and does so while retaining ease of manufacture, dependability and relatively low cost.